From 2b35b18d8c94198be14d0efbd02929f5658ebf63 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb@suse.de>
Date: Fri, 16 Feb 2007 01:28:38 -0800
Subject: [PATCH] --- yaml --- r: 48621 b: refs/heads/master c:
 29dbb3fc8020f025bc38b262ec494e19fd3eac02 h: refs/heads/master i:   48619:
 05a3227c187b09ec764cdaffabf0f8af3b3073b8 v: v3

---
 [refs]             |  2 +-
 trunk/mm/filemap.c | 32 +++++++++++++++++++-------------
 2 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/[refs] b/[refs]
index 51c705a95cac..5c37af8d89b4 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 3160a711ef754758e7f85ae371cf900252c1a392
+refs/heads/master: 29dbb3fc8020f025bc38b262ec494e19fd3eac02
diff --git a/trunk/mm/filemap.c b/trunk/mm/filemap.c
index 00414849a867..d1060b8d3cd6 100644
--- a/trunk/mm/filemap.c
+++ b/trunk/mm/filemap.c
@@ -2079,21 +2079,27 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
 		/* Limit the size of the copy to the caller's write size */
 		bytes = min(bytes, count);
 
-		/*
-		 * Limit the size of the copy to that of the current segment,
-		 * because fault_in_pages_readable() doesn't know how to walk
-		 * segments.
+		/* We only need to worry about prefaulting when writes are from
+		 * user-space.  NFSd uses vfs_writev with several non-aligned
+		 * segments in the vector, and limiting to one segment a time is
+		 * a noticeable performance for re-write
 		 */
-		bytes = min(bytes, cur_iov->iov_len - iov_base);
-
-		/*
-		 * Bring in the user page that we will copy from _first_.
-		 * Otherwise there's a nasty deadlock on copying from the
-		 * same page as we're writing to, without it being marked
-		 * up-to-date.
-		 */
-		fault_in_pages_readable(buf, bytes);
+		if (!segment_eq(get_fs(), KERNEL_DS)) {
+			/*
+			 * Limit the size of the copy to that of the current
+			 * segment, because fault_in_pages_readable() doesn't
+			 * know how to walk segments.
+			 */
+			bytes = min(bytes, cur_iov->iov_len - iov_base);
 
+			/*
+			 * Bring in the user page that we will copy from
+			 * _first_.  Otherwise there's a nasty deadlock on
+			 * copying from the same page as we're writing to,
+			 * without it being marked up-to-date.
+			 */
+			fault_in_pages_readable(buf, bytes);
+		}
 		page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec);
 		if (!page) {
 			status = -ENOMEM;